1. Field of the Invention
This invention relates to guide rollers and pinch rollers for guiding tapes of tape recorders and video tape recorders, and also other small rollers used for guiding soft tapes and printer tapes of computers, word processors, etc.
2. Prior Art
FIG. 10 shows a small roller A, which may be used as a guide roller or a pinch roller for guiding magnetic tapes of a tape recorder or a video tape recorder. The small roller A consists of a light metal cylinder 1 and an elastic rubber layer 2 provided thereon. The light metal cylinder 1, which may be made of aluminum, is fitted on a shaft 3 via a super-small ball bearing 4 or a radial bearing. Oil seals 5 are provided on the opposite sides of ball bearing 4. The small roller A is automatically tiltable in a small range of about 1.degree. or below with respect to the shaft 3.
Although a super-small ball bearing 4 of high precision has recently been manufactured by mass production, it does not meet user's requiement as to production costs. Further, because it is a type of radial bearing, it does not meet optimum requirements by users especially in having a automatically tiltable property. The reason why the radial bearings are utilized in this field is only that they happen to provide an automatic tilting action, although the action is done at a relatively narrower range.
Further, since the radial ball bearings require inner and outer rings 6 and 7, it is impossible to reduce the outer diameter of such rollers, and therefore, it is impossible to substantially reduce the size of apparatus utilizing these ball bearings.
Recently, rollers using tetrafluoride resins as bearing material have been announced. However, such rollers are incapable of automatic tilting because they are of slide bearing support type, and hence they can not be used as small rollers of the said type requiring automatic tilting property.
Further, in the aspect of a PV value and coefficient of friction, materials having high mechanical strength are liable to cause wear of the opposing member, and they also cause heat generation. (The PV value is obtained by multiplying P and V, where P=unit pressure of the shaft on the bearing that is obtained by dividing the load on the bearing by the projected bearing area. V=velocity of wear surface). Materials having low coefficient of friction, on the other hand, have insufficient mechanical strength. Therefore, both of such materials can be hardly used as small rollers of the type noted above.
Particularly, rollers used for guiding video tape recorder tapes have to meet strong demands for high speed rotation, capability of being used for long time, light weight (use of aluminum shaft), freedom from lubrication, prevention of heat generation, low noise and low cost. Development of a small roller which can meet the above demands has been expected in the pertinent field.